This invention relates to a system and method for modulating a frequency signal through frequency-shift keying.
Frequency-shift keying (FSK), sometimes referred to as frequency-shift modulation or frequency-shift transmission, is a form of modulation in which the modulating wave shifts the output frequency between two predetermined values corresponding to digital values 0 and 1. FSK has been used to modulate unique codes or other information onto frequency signals for remotely controlling systems such as vehicle remote keyless entry systems, garage door openers, estate gate openers, home security systems, etc. The unique codes may be encrypted or rolled.
In the prior art, frequency-shift keying has be achieved by installing a varactor in series with the output of an oscillator circuit producing a frequency signal. A varactor is a semiconductor device, such as a diode, in which the capacitance of the device varies with the applied voltage. Thus, applying an analog voltage to the varactor varies the capacitance of the varactor thereby altering the total capacitance of the oscillator circuit and shifting the signal between two different frequency values.
Although this method of frequency-shift keying has been routinely employed, it has shortcomings. Foremost, varactors are relatively expensive and significantly increase the cost of the FSK circuitry. Accordingly, there is a need for a reliable and less expensive system and method for modulating a frequency signal through frequency-shift keying.